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SubjectRe: [PATCH] device_cgroup: Roll back to original exceptions after copy failure
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Hi, Paul
Can this patch be applied or something to improve?

Thanks

on 2022/10/28 19:19, Paul Moore wrote:
> On Tue, Oct 25, 2022 at 7:02 AM Wang Weiyang <wangweiyang2@huawei.com> wrote:
>>
>> When add the 'a *:* rwm' entry to devcgroup A's whitelist, at first A's
>> exceptions will be cleaned and A's behavior is changed to
>> DEVCG_DEFAULT_ALLOW. Then parent's exceptions will be copyed to A's
>> whitelist. If copy failure occurs, just return leaving A to grant
>> permissions to all devices. And A may grant more permissions than
>> parent.
>>
>> Backup A's whitelist and recover original exceptions after copy
>> failure.
>>
>> Fixes: 4cef7299b478 ("device_cgroup: add proper checking when changing default behavior")
>> Signed-off-by: Wang Weiyang <wangweiyang2@huawei.com>
>> ---
>> security/device_cgroup.c | 33 +++++++++++++++++++++++++++++----
>> 1 file changed, 29 insertions(+), 4 deletions(-)
>
> On quick glance this looks reasonable to me, but I'm working with
> limited time connected to a network so I can't say I've given this a
> full and proper review; if a third party could spend some time to give
> this an additional review before I merge it I would greatly appreciate
> it.
>
>> diff --git a/security/device_cgroup.c b/security/device_cgroup.c
>> index a9f8c63a96d1..bef2b9285fb3 100644
>> --- a/security/device_cgroup.c
>> +++ b/security/device_cgroup.c
>> @@ -82,6 +82,17 @@ static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
>> return -ENOMEM;
>> }
>>
>> +static void dev_exceptions_move(struct list_head *dest, struct list_head *orig)
>> +{
>> + struct dev_exception_item *ex, *tmp;
>> +
>> + lockdep_assert_held(&devcgroup_mutex);
>> +
>> + list_for_each_entry_safe(ex, tmp, orig, list) {
>> + list_move_tail(&ex->list, dest);
>> + }
>> +}
>> +
>> /*
>> * called under devcgroup_mutex
>> */
>> @@ -604,11 +615,13 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
>> int count, rc = 0;
>> struct dev_exception_item ex;
>> struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
>> + struct dev_cgroup tmp_devcgrp;
>>
>> if (!capable(CAP_SYS_ADMIN))
>> return -EPERM;
>>
>> memset(&ex, 0, sizeof(ex));
>> + memset(&tmp_devcgrp, 0, sizeof(tmp_devcgrp));
>> b = buffer;
>>
>> switch (*b) {
>> @@ -620,15 +633,27 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
>>
>> if (!may_allow_all(parent))
>> return -EPERM;
>> - dev_exception_clean(devcgroup);
>> - devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
>> - if (!parent)
>> + if (!parent) {
>> + devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
>> + dev_exception_clean(devcgroup);
>> break;
>> + }
>>
>> + INIT_LIST_HEAD(&tmp_devcgrp.exceptions);
>> + rc = dev_exceptions_copy(&tmp_devcgrp.exceptions,
>> + &devcgroup->exceptions);
>> + if (rc)
>> + return rc;
>> + dev_exception_clean(devcgroup);
>> rc = dev_exceptions_copy(&devcgroup->exceptions,
>> &parent->exceptions);
>> - if (rc)
>> + if (rc) {
>> + dev_exceptions_move(&devcgroup->exceptions,
>> + &tmp_devcgrp.exceptions);
>> return rc;
>> + }
>> + devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
>> + dev_exception_clean(&tmp_devcgrp);
>> break;
>> case DEVCG_DENY:
>> if (css_has_online_children(&devcgroup->css))
>> --
>> 2.17.1
>>
>
>

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